In the design of hearing aids, there is inherently a tradeoff between the functionality of the device on the one hand and its size and power requirements on the other hand. For example, it is known to include several signal processing channels in the design of a hearing aid, each channel separately processing a distinct band of audio frequencies. A device of this type can provide more flexible performance and, thus a better perceived performance among a group of users, having diverse hearing problems, than a device which amplifies all frequencies as a single band. In addition, the perceived performance among the group of users increases in direct proportion to the number of channels that are used, up to some limiting number. However, each channel that is added to a hearing aid increases the size of the device and its power consumption. Consequently, few hearing aids exist which use multiple frequency channels and those which do, use only a few channels.
In recent years, there has been a widespread use of linear very large scale integration (VLSI) in the design of hearing aids. These circuits allow a designer to increase the functionality of a hearing aid without significantly increasing its size. But this increase in functionality may be at the expense of an undesirable increase power consumption. VLSI devices have increased power consumption relative to smaller scale devices because they include a larger number of components. Moreover, one type of component, the amplifier, is often designed with a complex biasing network to overcome variations in performance that are attributable to variations in the processes used to produce the amplifiers. These biasing networks may trade inefficiencies in the use of the power source for consistent device performance.
The power requirements of a hearing aid are an important design parameter. Because hearing aid batteries are relatively expensive it is desirable for the hearing aid to use them efficiently. In addition, since the battery is one of the larger components of a hearing aid, it is desirable to design circuitry which uses few batteries as possible.